Explosive booster



Jan. 29, 1952 HIR. WRIGHT ETAL 2,583,802

EXPLOSIVE BOOSTER Filed Dec. 16. 1948 FIG.- I

FIG 2 Inventors HAROLD REGINALD WRIGHT ROGER WILLIAM MARTYN Attorneys Patented Jan. 29, 1952 EXPLOSIVE BOOSTER Harold Reginald Wright, West Kilbride, and

Roger William Martyn, Fairlie, Scotland, assignors to Imperial Chemical Industries Limited, a corporation of Great Britain Application December 16, 1948, Serial No. 65.55%

In Great Britain March 1, 1948 Claims. i

The present invention is concerned with a new or improved form of explosive booster, and has-for an object to provide a detonating explosive booster adapted for use under conditions of high hydrostatic pressure; as in deep well blasting.

In oil well blasting and the like blasting operations at a considerable depth below the surface it is frequently necessary to introduce into the borehole a series of explosive charges each supported in a container with its fore end closed and preferably nosed and its after end open. Under these conditions there is liable to be a certain thickness of liquid or semi-liquid material between the top of each explosive charge and the bottom of the explosive charge in the next container, so that the transmission of detonation from one explosive charge to the next may be rendered uncertain.

It would therefore be desirable to provide each explosive charge at its upper end with a booster comprising an explosive of the same order of sensitiveness as the customary explosive pellet boosters consisting of cyclonite, pentaerythritol tetra-nitrate, tetryl or the like, furnished with a detonator; but under high hydrostatic pressures the tubular container of an ordinary detonator is liable to be distorted with the result that the liquid can gain entry into and phlegmatise its explosive charges.

According to the present invention a booster of readiJy assembled construction suitable for use under conditions of considerable hydrostatic pressure comprises two threaded rigid cups of pressure-resisting wall construction screwed together to form a liquid-tight capsule wherein is contained a pellet charge of a solid high velocity detonating explosive channelled from end to end, and, occupying the channel with its closed end supported against the base of one of the cups and its open end pressed into a lining of resilient material at the closed end of the other cup, a detonator capable when itself exploded of initiating the detonation of said pellet charge and comprising a thin walled tube loaded under pressure with two superposed detonating explosive charges, whereof that at its closed end is the more sensitive to initiation by shock, the end wall of the rigid cup in contact with the closed end of the said thin walled tube being locally weakened so that although rigid under the prevailing hydrostatic pressure the weakened portion will be easily ruptured from without by the detonation of an explosive charge in its proximity.

In accordance with a preferred feature of the invention the external contour of the end wall of the cup-like member is recessed at the weakened portion.

It will be understood that in deep well blasting high temperatures as well as high hydrostatic pressures are commonly encountered, and as it is important that the explosive charges in the booster should remain solid, stable, and sensitive at the temperatures encountered it is pre ferred that the channelled pellet charge and the less sensitive of the charges of the detonator should be based on an explosive of melting point exceeding C., for instance cyclonite, if desired with a binder. The more sensitive explosive charge at the closed end of the detonator is preferably one comprising a heavy metal azide, e. g. lead azide. To assist the binding properties of the lead azide or to increase in 'sensitiveness to initiation alead salt of a polynitro-phenolic compound e. g. lead styphnate, may be admixed with the heavy metal azide. Under somewhat cooler conditions the less sensitive charge of the detonator and the pellet charge might consist essentially of pentaerythritol tetranitrate (melting point 139 C.) or even tetryl (melting point 128 C.).

The thin walled tube of the detonator should be slightly longer than the pellet charge, which advantageously is held between the end of the cup with the weakened wall and the resilient lining at the end of the other cup, so that when the cups are screwed together the open end of the detonator tube will bite into the resilient linin but the pellet will not be crushed. The detonator tube may be an easy sliding fit within the channel through the pellet. The hydrostatic pressure liable to be encountered may be of the order of 5 tons per square inch, and the cups are preferably made of steel. They may be provided externally with projections or flattened locally to assist their being threaded tightly together.

It will be understood that in rail or ship transport and magazine storage the detonators will be stored separately from the channelled pellet charges for reasons of safety. When, as is preferred, the weakened portions of the end wall of the cup of the booster contiguous to the closed end of the detonator tube has a recessed exterior contour the risk of any premature explosion taking place while a blasting explosive charge and the booster in contact with its upper end are being lowered into the wellhole is minimised, since the thicker portions of the metal bounding this recess tend to prevent any large stones that may fall down from striking the weakened portion of the end wall.

The invention is further illustrated with reterence to the diagrammatic drawings, accompanying the specification whereof Figure l is an axial section and Figure 2 is a section across the line AA in Figure 1 as viewed in the direction'oi the arrows.

In the drawings I is a thick walled rigid cup of pressure resisting metal with an internally plane end wall having a thin portion 12 around its axis opposite a recess formed in the exterior of the end wall, and having a longitudinal wall terminating in an internally threaded portion 2; 3 is a thick walled rigid cup made of pressure resisting metal whose longitudinal wall terminates in an externally threaded portion 4. 6 is a pellet primer composed essentially of a high melting explosive, such as cyclonite, made 'by compressing the explosive and having a longitudinal axial channel in which the detonator tube 1 is an easy sliding fit. 8 is a rubber disc and 9 is a gasket washer. Ill is a charge of a mixture of lead azide, lead styphnate and aluminium compressed into the closed end of the thin walled aluminium detonator tube 1 and II is a charge of cyclonite compressed over the more sensitive charge ID. The curved Wall of the cup I is locally flattened and there are projections 13 on the wall of the cup 3 to assist the threaded ends 2 and 3 being screwed together tightly enough to prevent any leakage of fluid into the booster under the conditions of its use, as well as ensuring that the pellet 6 is in contact with the rubber disc 8 and the slightly longer tube V bites into said disc and is thus held firmly in position.

We. claim:

1. A booster comprising two threaded rigid cups of pressure-resisting wall construction screwed together to form a liquid tight capsule, a lining of resilient material in the bottom of one of said cups, a pellet charge of a solid high velocity detonating explosive channelled from end to end and located within said capsule, and a detonator capable when exploded of initiating the detonation of said pellet and comprising a thin walled tube loaded under pressure with two superposed detonating explosive charges, said detonator occupying the channel with its open end pressed into said lining in the bottom of one of said cups and its closed end supported against the base or the other cup which is locally weakened so that although rigid under the prevailing hydrostatic pressure it will be easily ruptured from without by the detonation 01' an explosive charge in its proximity.

2. A booster as set forth in claim 1 wherein the external contour of the end wall of the cup member locally weakened is recessed at the weakened portion.

3. A booster as set forth in claim 1 wherein the superposed detonating explosive charge in that end of the tube adjacent the base of the unlined cup is the more sensitive explosive charge.

4. A booster as set forth in claim 1 wherein the thin walled tube oi! the detonator is slightly longer than the pellet charge and is held between the end of the cup with the weakened wall and the lining of resilient material at the end of the other cup so that when the cups are screwed together the open end of the detonator tube will bite into the resilient lining, but the pellet will not be crushed.

5. A booster as set forth in claim 1 wherein the pellet charge and the superposed detonating explosive charge nearer the open end of the thin walled tube are of cyclonite and the superposed charge adjacent the closed end of the tube is of heavy metal azide.

HAROLD REGINALD WRIGHT. ROGER WILLIAM MARTYN.

REFERENCES CITED The following references-are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,297,499 Rushmore Mar. 18, 1919 2,464,650 Pass et a1. Mar. 15, 1949 FOREIGN PATENTS Number Country Date 24,305 Great Britain of 1914 

